FIG. 1 diagrammatically illustrates the configuration of a guided acoustic travelling wave lens device--one that employs a relatively narrowly dimensioned traveling wave channel--as comprising a laser 10, the optical beam output 11 of which is focussed by a cylindrical lens arrangement 12 and deflected by a mirror 13 onto an acousto-optic beam deflector 14, to which an RF input signal is applied. The acousto-optically modulated beam is then reimaged by a further spherical--cylindrical lens arrangement 15 onto a traveling lens cell 16, that contains a traveling wave lens transport medium 17 and a traveling wave lens launching transducer 18. The scanned beam is then imaged onto an image collection medium, such as a photographic film 19.
In a number of applications, the acousto-optic waveguide may be configured as a reduced height, guided acoustic travelling wave lens (ATWL) waveguide device, such as that diagrammatically illustrated at 30 in FIG. 2. In this type of acoustic wave guide architecture, a first end 32 of the waveguide has an acoustic wave input aperture 34 (to which an acoustic wave-launching piezo-electric transducer is coupled), at an input end of a relatively narrow (fluid-containing) channel 36, having a cross-section of width w and height h, where w&gt;&gt;h.
For a non-limiting illustration of examples of documentation describing such guided acoustic traveling wave lens devices, attention may be directed to an article entitled: "Optical Beam Deflection Using Acoustic-Traveling-Wave Technology," by R. H. Johnson et al, presented at the SPIE Symposium On Optical, Electro-Optical, Laser and Photographic Technology, August 1976, FIG. 6 of which corresponds to FIG. 1, above, an article entitled: "Guided acoustic traveling wave lens for high-speed optical scanners," by S. K. Yao et al, Applied Optics, Vol. 18, pp 446-453, February 1979, and the U.S. Pat. No. 3,676,592 to Foster.
In a reduced height guided wave device, because the acoustic transmission properties of the acoustic propagation medium (fluid) within the waveguide channel 36 are considerably different from those of the transducer being used to launch the acoustic wave into the waveguide, there is a substantial acoustic impedance mismatch between the transducer and the waveguide. Indeed, the acoustic impedance of the waveguide may be on the order of twenty or more times that of the transducer.
In such a circumstance, in order to provide significant energy coupling from the transducer to the waveguide's acoustic propagation medium (e.g. water), the transducer must be allowed to resonate to very large internal power. This causes two problems. First, the acoustic transducer is prone to failure, as the result of the very substantial acoustic stresses required. Second, the bandwidth is limited.